Ineffective (adjective)

1. Not producing the intended or desired effect.
2. Not producing results or having the desired impact.
3. Not achieving the desired outcome.

Origin:

From in- ("not") + effective.

Examples:

1. The medication was ineffective in treating the disease.
2. The policy was ineffective in controlling the problem.
3. The strategy was ineffective in achieving the goals.
4. The leader was ineffective in motivating the team.
5. The teacher's methods were ineffective in teaching the students.